The invention relates to a magnetic head, and more particularly, to a magnetic head for use in a tape recorder, a video tape recorder (VTR) or the like which achieves a high density recording by establishing a remanence in the direction of thickness of a magnetic record medium such as magnetic tape.
Ordinarily, the technique to record information signal on a magnetic record medium such as magnetic tape generally comprises bringing a magnetic head into contact with the surface of the medium to establish a remanence therein in a direction parallel to the surface of the medium. According to this technique, the head has its poles located opposite to each other with a narrow air gap therebetween so that a leakage flux from the gap is bypassed through the medium. Because the leakage flux passes through the medium in a direction parallel to its surface, the magnetizable material contained in the medium is magnetized in a direction parallel to the surface of the medium, with its remanence defining a magnetic recording. With the described magnetic recording technique, it is known that considerations of the air gap of the magnetic head and the frequency of the signals being recorded impose a limitation on the recording density of information signal.
Recently, a variety of recording techniques have been proposed which drastically improves the recording density by a so-called vertical magnetization scheme in which a remanence is established in the medium in a direction perpendicular to the surface thereof or in the direction of its thickness. This technique employs a magnetic record medium having an easy axis of magnetization in a direction perpendicular to the surface. Referring to FIG. 1, there is shown a magnetic record medium 6 comprising a base film 6c of polyester, for example, carrying an upper layer 6b of high permeability material and a layer 6a coated thereon which is formed of a magnetizable material having an easy axis of magnetization in a direction perpendicular to the surface.
FIG. 1 also shows a magnetic head 1 which may be used for recording a signal in such medium. Specifically, the head 1 comprises a magnetic head core 2 of a magnetizable material such as ferrite which has an inverse U-configuration, and a coil 3 disposed thereon. The core 2 includes one limb 4 which has its free end tapered, with its end face defining a narrow rectangle which is elongate in a direction perpendicular to the direction of movement of the record medium and forming a pole 4a for recording and/or playback. This end face is adapted to be disposed in abutment against the medium. The core has its other limb 5 which has an increased thickness to present an increased cross-sectional area, thus reducing its reluctance.
In operation, when a signal current is passed through the coil 3 as the medium 6 moves to the left, as viewed in FIG. 1, relative to the head 1, flux 7 is produced within the core 2 as indicated by dotted line, and passes from the pole 4a vertically through the layer 6a and passes through the layer 6b in a direction perpendicular to the surface and returns to the limb 5, thus forming a closed magnetic path. It will be seen that as the flux passes vertically through the portion of the layer 6a which is located opposite to the pole 4a, a remanence is produced therein in a direction perpendicular to the surface, and because the pole 4a has a reduced width, a high flux density is produced. In a region of the layer 6a which is located opposite to the limb 5, the flux density is greatly reduced because of an increased area of the end face of the limb 5, so that no substantial or effective magnetization occurs in this region of the layer 6a. As the medium 6 continues to move to the left relative to the head 1, a pattern of the remanence corresponding to the signal current is recorded in the top layer 6a, thus achieving a magnetic recording.
During the playback operation, the poles 4a and 5a of the magnetic head 1 are disposed close to or in abutment against the medium 6 in which the signal is recorded, and the latter moved in a direction perpendicular to the plane of the drawing. The remanence recorded in portions of the layer 6a which are located opposite to the poles 4a, 5a produces a flux to pass through the core 2 and the layer 6b, thus closing a magnetic path. The flux following the closed magnetic path links with the coil 3, producing a playback current therein in accordance with a change of the remanence in the layer 6a as medium 6 moves. The magnetic head 1 however has a tracking difficulty in that it is difficult to align the head 1 with the medium 6. As a consequence, extraneous signals other than the recorded signal which is to be reproduced may be picked up, thus causing noises.
There has also been proposed a magnetic head for vertical magnetization recording which has an inverted U-configuration as the head 1, but which has one limb having a free end of a greatly reduced width than the other limb so as to serve as a recording pole to achieve a high density recording. Referring to FIG. 2, magnetic head 11 includes a magnetic head core 12 having an inverted U-configuration, and a coil 13 disposed thereon. One limb of core 12 is used for recording or playback purpose while the other limb 15 has a reduced reluctance. The free end of the limb 14 is tapered to a sharp edge which defines a record/playback pole 14a. The pole 14a is in the form of a rectangle having a reduced width, with its lengthwise direction being disposed at right angles to the direction of movement of medium 6 (see FIG. 1).
When the coil 13 is energized with a signal current to be recorded and the medium 6 runs, a recording flux is produced within the core 12, creating a strong remanence in a portion of the layer 6a which is located opposite to the pole 14a. In this manner, a high density recording is achieved. The flux density is reduced in a region of the layer 6a which is located opposite to the end face of the limb 15 which has an increased area, whereby no substantial magnetization occurs in this region of the layer 6a. During the playback operation, the pole 14a and the end face of the limb 15 are disposed opposite to the medium 6. The remanence recorded in the medium 6 follows a closed path including the core 12, and hence as the medium 6 is moved relative to the core 12, a playback current is produced in the core 13.
The magnetic head 11 suffers from the same disadvantage as the magnetic head 1. In addition, the limb 15 may pick up extraneous signals other than the intended recorded signal. Specifically, though it has been described previously that the flux which passes through a portion of the layer 6 opposite to the end face of the limb 15 during the recording process has a reduced density, it does have a certain degree of magnetization. The area of the end face of the limb 15 is by orders of magnitude greater than that of the pole 14a. As the signal is continuously recorded in the layer 6 from the pole 14a, the latter successively faces unrecorded regions of the layer 6a, but only a very limited area of the end face of the limb 15 faces an unrecorded region of the layer 6a while the remainder of the end face of the limb 15 faces an already recorded region of the layer 6a. Consequently, a magnetization of the region of the layer 6a which is located opposite to the limb 15 occurs repeatedly, though of a reduced magnitude. Thus, there exists a remanence of a reduced magnitude as a result of a repeated recording in the region of the layer 6a located opposite to the limb 15, and during the playback, it may be picked up simultaneously with the desired recorded signal, causing noises.